Issue 52

S. Budhe et alii, Frattura ed Integrità Strutturale, 52 (2020) 137-147; DOI: 10.3221/IGF-ESIS.52.12

    

Tresca

1 2 , 3 1 1 , 2 2 

k

Von Mises

  

ASSY

.

The strain hardening exponent is determined based on the Hollomon (power-law) model [27] and the Ramberg-Osgood model [28] for failure analysis of pipeline. Corroded pipelines The basic model of the pipe to determine the theoretical burst pressure is extended to the corroded (damage/defect) metallic pipeline. The general equation of the burst pressure for a pipeline with a corrosion defect is as follows:

t

th max





(2)

P

flow



r 

i

where the flow stress ( flow  ) represents the flow stress of the pipe material and   is a remaining strength function (i.e. damage factor) which represents the strength reduction of the pipelines due to the corrosion. There are many semi-empirical models available in the literature however a careful selection of the model is very important as both flow stress and remaining strength values differ with respect to the model.

R EMAINING STRENGTH OF CORRODED PIPELINES

A

n accurate representation of defect geometry and defect shape of the damaged pipeline is useful for a better prediction of the remaining strength capacity of the pipe. Natural corrosion is the main source of localized damage of metallic pipelines, hence, defect size and shape is quite different from case to case. Generally, a non- uniform nature of corrosion occurs as shown in Fig 1(a) and to represent the actual defect shape for analysis is quite difficult. In most of the semi-empirical models (Tab. 1), the defect shapes are idealized as rectangular, parabolic, elliptical, mixed or effective area shape. Researchers often used a controlled metal wall loss using a machined process on a metal tube to replicate the actual corrosion defect and one such example is rectangular defect as shown in Fig 1(b) [12].

Figure 1: Metallic pipeline (a) with actual corroded defect [27] (b) machined defect to represent corroded damage [12].

Metal wall loss defects (rectangular, parabolic, etc.) in metallic pipelines are taken into account by the remaining strength factor ( )   for prediction of strength capacity of a corroded pipe. The general form of strength prediction of defective pipelines is as:

  

P r t

i

(3)

  



 







undamaged

139